1. Field of the Invention
The present invention relates to a thermally conductive resin sheet which is used for conducting heat from a heat generating part into a heat dissipating member in electric or electronic appliances or the like. In particular, the invention relates to an insulating thermally conductive resin sheet which conducts heat of a power module into a heat dissipating member and to a power module using this thermally conductive resin sheet.
2. Description of the Related Art
In thermally conductive resin film layers for conducting heat from a heat generating part into a heat dissipating member in an electric or electronic appliance, there have hitherto been widely used thermally conductive resin compositions having an inorganic filler added to a thermosetting resin in view of requirements of high thermal conductivity and insulation properties.
For example, in a power module, there is a sheet or coating film made of a thermosetting resin containing an inorganic powder as a thermally conductive insulating layer to be provided between the back surface of a lead frame having a power semiconductor device mounted thereon and a metal plate which becomes a heat dissipating part (see, for example, JP-A-2001-196495, page 3 and FIG. 1).
Also, for example, there is a sheet made of a thermosetting resin composition having a highly thermally conductive inorganic filler blended therein as a thermally conductive resin composition which is mediated between a heat generating electronic part such as CPU and a heat dissipating fin (see, for example, JP-A-2002-167560 (page 3 and FIG. 1)).
Following miniaturization of electronic appliances or enhancement in the performance of electronic parts, the amount of heat generation from electronic appliances or electronic parts greatly increases, and thermally conductive resin sheets for conducting heat from a heat generating part to a heat dissipating part in the electric or electronic appliance are required to have higher thermal conductivity.
In conventional insulating thermally conductive resin sheets in which a highly thermally conductive inorganic filler is added to a thermosetting resin, the thermal conductivity is improved by increasing the content of the inorganic filler to be added. However, an increase of the content of the inorganic filler is limited from the standpoint of the production of thermally conductive resin sheets. In addition, there was involved such a problem that it is impossible to obtain an insulating thermally conductive resin sheet having a larger coefficient of thermal conductivity.
Also, in power modules in which the foregoing conventional insulating thermally conductive resin sheet is provided between the heat generating part having a power semiconductor device mounted thereon and a heat sink as a heat dissipating part, there was encountered such a problem that the miniaturization and enhancement in the capacity are limited.